J.M. Gómez de Salazar

High temperature soldering of SiC particulate aluminium matrix composites (series 2000) using Zn–Al filler alloys

Abstract The present paper evaluates the solderability of three discontinuously reinforced aluminium matrix composites. The tested composites were an aluminium alloy of the 2000 series (AA2014) reinforced with different percentages of silicon carbide particles (6, 13, and 20 vol.-% respectively). A similar study was carried out on the unreinforced aluminium alloy for comparative purposes. Three low temperature filler alloys of the Zn–Al system were used for soldering. Drop formation tests were performed to evaluate the wettability of the molten filler alloys and sample joints (single overlap specimens) were produced to determine solder penetration in the joint clearance. Microstructural studies of the joints were carried out to determine the effects of the solid reinforcement particles on molten pool behaviour and solidification mechanisms.

Dissimilar fusion welding of AA7020/MMC reinforced with Al2O3 particles. Microstructure and mechanical properties

Abstract Metal matrix composites reinforced with Al 2 O 3 particles combine the matrix properties with the ceramic properties of the reinforcement. However, its wide application as structural materials need of the proper development of their joining processes. The present work describes the results obtained from microstructural (Optical and scanning electron microscopy and electron probe microanalyser) and mechanical evaluation (hardness and tensile tests) of aluminum matrix composites (AA7005) reinforced with 10% vol. fraction Al 2 O 3 particles (W7A10), welded to the unreinforced alloy AA7020 (Al–Zn–Mg), using metal inert gas welding process using ER4043 (Al–Si) and ER5356 (Al–Mg) as fillers. The thermal effect of welding on different types of joint results in a loss of the mechanical properties in the heat affected zones. These properties could be recovered with post-welding heat treatments.

Special features of the formation of the diffusion bonded joints between copper and aluminium

A metallographic study of diffusion bonds between aluminium and copper has been made in order to further understanding of the mechanism of bond formation for joints between dissimilar metals that form intermediate phases or intermetallic compounds. A three-stage mechanistic model based upon sintering principles has been proposed to explain this kind of diffusion joint.

Diffusion bonding of Ti-6Al-4V alloy at low temperature: metallurgical aspects

The diffusion bonding of the Ti-Al-4V alloy at low temperature (850°C) has been studied. The principal objective of this investigation was the development of a diffusion bonding procedure suitable for Ti-6Al-4V alloy and capable of being used as part of a superplastic forming/diffusion bonding process. It was found that high-quality joints can be obtained by bonding at 850°C, with pressures of 4 MPa and times in the range 90–120 min. Mechanical properties of the joints were determined using cylindrical and plane test pieces. Tensile, shear and peeling tests were used to determine the strength of the joints. On bonding with the above conditions, the parent alloy strength was reached. Little reduction in these values was measured because the heat treatment was applied during bonding. A metallographic study by scanning electron microscopy and energy dispersive spectroscopy was performed to determinate the influence of the previous parameters on the microstructural changes that occur in the joint. Grain growth kinetics and ratio of bonding area were also studied. The results shows that a new method of diffusion bonding for Ti-6Al-4V alloy has been developed. This method can be carried out using lower bonding temperatures than in conventional processes.

Diffusion bonding of an aluminium-copper alloy reinforced with silicon carbide particles (AA2014/SiC/13p) using metallic interlayers

In this work, the application of solid state diffusion bonding to a SiC particulate reinforced aluminium-copper alloy (AA2014) has been studied. The use of metallic interlayers such as an aluminum-lithium alloy and pure silver, has been tested. Bonding interfaces were microstructural characterized using scanning electron (SEM) and transmission electron microscopies (TEM). Joint strengths were evaluated by shear mechanical tests, completed with fractographic studies to determine the failure mechanisms of each kind of joint.

Crystal structure of BaGd2NiO5 prepared by reaction of Ni metal with BaCO3 and Gd2O3

Abstract Black prismatic crystals of BaGd2NiO5 were grown by reaction of an excess of Ni metal with a mixture of BaCO3 and Gd2O3, Ba:Gd=2:1, after heating in air at 1100°C for three days and slowly cooling. BaGd2NiO5 is orthorhombic, a=3.7872(4), b=5.8388(9), c=11.498(1) A , V=254.25(10) A 3 , Z=2, D c =7.71 g cm −3 , F (000)=504, μ( MoK α)=371.6 cm −1 , S.G. Immm (No. 71), T=295 K, and R=0.019 for 223 observed reflections. The crystal structure can be conceived as the result of packing the metallic coordination polyhedra: BaO10 bicapped quadrangular prisms, GdO7 capped trigonal prisms, and chain-forming NiO6 flattened octahedra.

Diffusion bonding of alumina to steel using soft copper interlayer

The diffusion bonding of a low steel to alumina has been studied in the present work. Thin foils of a soft metal (copper) were used to reduce the effects of the residual stresses produced in the joint by thermal expansion mismatch. The strength of the joint was found to be influenced by the bonding parameters, but principally by the oxygen content both on the surface and in the copper matrix. The diffusion bonds have been mechanically tested using a three-point bending test. Maximum bending strengths of 100 MPa were achieved by using a 0.1 mm copper foil, and bonding in a oxidizing atmosphere (PO2=104Pa). SEM and EDS investigations have shown the presence of reaction products in the copper-alumina interface which controls the mechanical properties of the joint.

Diffusion bonding of grey cast iron to ARMCO iron and a carbon steel

The microstructure transformations produced during the diffusion bonding of grey cast iron to pure iron (ARMCO iron) and to a hypoeutectic steel (0.55% C) have been studied. The indirect determination of the carbon concentration profiles has produced a diffusion equation that relates the microstructure of the bond interface to the bonding temperature and time. A new tensile test specimen is described; this specimen has a variable circular section which allows the determination of true tensile strength of dissimilar diffusion bonds. Metallographic and fractographic studies have shown that the optimum bonding conditions for both types of joint are a bonding temperature at 980° C, for 5 min at a bonding pressure of 4.5 MPa.

Diffusion bonding of an aluminium-lithium alloy (AA8090) using aluminium-copper alloy interlayers

Diffusion bonds have been produced between sheets of an Al-Li-Cu-Mg-Zr alloy using aluminium-4% copper vapour deposited metallic interlayers. Microstructural changes occurred both in the parent alloy and in the bond interface after diffusion bonding cycles and post-bonding heat treatments were analysed. Different metallographic techniques (light microscopy, scanning and transmission electron microscopy) have been used. Diffusion bonding trials were carried out using the same alloy (AA8090), both in non-superplastic (T6) and superplastic conditions. Differences in their behaviours in relation to diffusion bonding were observed.

Crystal growth of Ba2Cu3RO7 − x (R = Y, Nd, Gd, Yb)

Abstract Two methods of growing Ba 2 Cu 3 RO 7 − δ ( R = Y , Nd, Gd, Yb) crystals were followed. In the first method a molten and water quenched mass of molar ratios Ba : Cu : R = 2 : 3 : 1 is introduced into the furnace at 1040°C, soaked at this temperature for 5 h and cooled at 25°C h -1 . In the second, a mixture of CuO and BaO 2 (72 : 28) is employed as a flux and the crystals are grown by cooling from 1010°C at 5°C h -1 or 15°C h -1 . CuBaR 2 O 5 crystals are also grown. The first method leads to euhedral crystals, better formed than those grown using fluxes. The shape and growth mode of the crystals grown by the second method are accounted for by the presence of helicoidal dislocations of the same sign or by means of a Frank-Read mechanism. X-ray diffraction data for BaCuGd 2 O 5 and Ba 2 Cu 3 GdO 7 − x are included.